Hi there, I noticed a "conflicting declaration" error when developing a program which uses Boost.Program_Options and Boost.Type_Erasure. Further investigation showed me, that the conflict is actually between Boost.Iterator and Boost.Type_Erasure. A test-case which demonstrates this compiler-error is the following simple two-liner: #include <boost/type_erasure/iterator.hpp> #include <boost/iterator/iterator_adaptor.hpp> Clang is quite verbose and outputs the following: /tmp/boost-1_58/boost/iterator/iterator_adaptor.hpp:44:18: error: target of using declaration conflicts with declaration already in scope using iterators::use_default; ^ /tmp/boost-1_58/boost/iterator/iterator_adaptor.hpp:40:10: note: target of using declaration struct use_default; ^ /tmp/boost-1_58/boost/type_erasure/iterator.hpp:27:8: note: conflicting declaration struct use_default; ^ 1 error generated. The fix is actually quite simple and should be applied to Boost.Iterator. I already provided a pull-request [1] for this. I hope this fix can still make it into the upcoming 1.59 release of Boost. Best regards, Deniz Bahadir [1] https://github.com/boostorg/iterator/pull/15 -- BENOCS GmbH Dipl.-Inform. Deniz Bahadir Winterfeldtstr. 21 10781 Berlin Germany Phone: +49 - 30 / 577 0004-22 Email: deniz.bahadir@benocs.com www.benocs.com Board of Management: Michael Wolz, Dr.-Ing. Oliver Holschke, Dr.-Ing. Ingmar Poese Commercial Register: Amtsgericht Bonn HRB 19378